Photographic transfer process



April 3, 1956 H. c. YUTZY ETAL 2,740,717

PHOTOGRAPHIC TRANSFER PROCESS Filed May 3, 1952 SUPPORT GEM TINO -SILVER HAL/DE I2 EMULSIONCONMl/V/NG /vo/v .;/\o/rFus//vs DEVELOP/N6 AGE/VT I EXPOSED II 12 EXPOSED l DEVELOPMENT RECEIVING SUPPORTCONM/IV/NG SILVER #4 1.105 SOLVENT AND I5 PREC/P/MTl/VG AGENT TRANSFE RRE D IMA GE EMULSION cum DEVELOP/N6 AGE/V7 Henry C y f SUPPORT Edaiardtf )izckel I N V EN TORS BY RECEIVING LAYER 7W1 ATTORNEYS United States Patent 2,740,717 PHOTOGRAPHIC TRANSFER PROCESS Henry C. Yutzy and Edward C. Yackel, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application May 3, 1952, Serial No. 285,856 5 Claims. (Cl. 95-88) This invention relates to photography and particularly to a photographic transfer process for use in the reproduction of line or printed material or continuous tone images.

Processes for the preparation of direct positive images by transfer procedures have been described in the literature. These methods involve in general the development of an exposed silver halide emulsion layer to metallic silver in the usual way, the transfer of the residual undeveloped silver halide from the unexposed areas by means of a silver halide solvent in the developer to a receiving sheet pressed in contact with the negative. The receiving sheet bears development centers upon which the dissolved silver halide or silver halide complex is deposited as metallic silver by physical development, using the chemical energy from the conventional photographic developing agents to effect this physical development. Various modifications have been described in which the steps were carried out separately or in combination, the prior art having been discussed in an article by Varden in Journal of the Photographic Society of America, vol. 13, September 1947, page 551.

The prior art processes involve development in the conventional silver halide developer solutions containing Elon or hydroquinone, and usually containing sodium thiosulphate. In processes of this type where a solvent and diffusing developing agent is used, considerable difficulty has been encountered in obtaining stable positive prints. Permeation of the receiving sheet by the developing agent leaves developer in the final print and this oxidizes in the air to yield a stain. This may be overcome by Washing the final print, but in the simplified procedures which are desirable this is of course objectionable. The difiiculty may be partially avoided by inclusion of acid materials in the receiving sheet, but this leads to the necessity for delicate chemical balance during processing and is necessarily critical.

It is therefore an object of the present invention to provide a simplified photographic transfer process for the production of direct positive images. A further object is to provide a direct positive transfer process in which the formation of stain in the receiving sheet is avoided. A still further object is to provide a transfer process in which the developing agent is not permitted to permeate and stain the non-image portions of the receiving sheet. Other objects will appear from the following description of our invention.

These objects are accomplished by the use as the sensitive material of hardened colloid-silver halide emulsion layers containing developing agents of relatively high molecular weight, low solubility and low tendency to diffuse so that they are substantially non-diffusing in the colloid of the emulsion layer during the processing steps. The exposed emulsion is then developed in a simple alkaline solution and immediately pressed into contact with a light insensitive receiving support in the presence of a silver halide solvent and a precipitating agent to convert unexposed and dissolved silver salt to an insoluble form. The emulsion must be pressed onto the receiving sheet while wet or moist, although excess liquid may first be removed. After remaining in contact for a short time the sheets are peeled apart and a positive image is obtained in the re ceiving sheet which shows little tendency to exhibit stained highlights as a result of oxidation of residual developing agent in the print.

In the accompanying drawing,

Fig. l is a cross-sectional view of our material at successive stages in the process, and

Fig. 2 is a sectional view of a roll fihn employing our process.

According to the preferred embodiment of our invention we use as the light-sensitive material a hardened colloid-silver halide emulsion, e. g. a gelatin emulsion, coated on film, paper or other support. The emulsion contains a substantially non-diffusing developing agent which may be either of the tanning or non-tanning type. The sensitive layer is exposed to an object or image, usually a line or halftone image although a continuous tone image may also be used to form the record in the sensitive layer. Exposure may be made directly on the emulsion of the sensitive element or by reflex printing. The exposed element is then developed by immersion in a dilute alkaline solution such as dilute sodium carbonate or sodium hydroxide, which may contain well-known fog restrainers such as soluble bromide, antifoggants, etc., and while wet with this solution is pressed into contact with a receiving sheet of paper or other material in the presence of a silver halide solvent and a precipitating agent. It is convenient in most cases to incorporate both the silver halide solvent and the precipitating agent in the receiving sheet although either or both may be incorporated in a separate solution used to treat the negative material after development. After being in contact for about 5 seconds to a minute or more the negative material is then stripped away and a positive image is found in the transfer sheet with which it was in contact, the positive image representing the unexposed portions of the negative.

The following compounds illustrate the developing agents which may be incorporated in the sensitive emulsion:

3,4 dihydroxy diphenyl 2,5 -dihydroxy diphenyl 2,3-dihydroxy diphenyl 5,6,7,8-tetrahydronaphthohydroquinone 2-hydroxy-5-amino diphenyl 3,4-diaminodiphenyl Dodecyl catechol Diamyl hydroquinone Lauryl hydroquinone Suitable silver halide solvents which may be used according to our invention are as follows: Ammonium hydroxide Ammonium chloride Ammonium sulfate Ammonium nitrate Sodium thiosulfate Sodium sulfite Thiocyanates of alkali metals Suitable precipitating agents which may be used according to our invention are as follows:

Sodium sulfide or selenide Zinc sulfide Amino guanidine sulfate Amino guanidine carbonate Arsenous oxide Sodium stannite Thiourea and its derivatives Substituted hydrazines Organic sulfiding agents, e. g. mercaptans Xanthates The precipitating agent should not produce a strong tint in the paper in its oxidized or reduced forms. The agent itself should preferably. be white, as zinc sulfide, or slightly colored, as manganese sulfide. It should be present in sufficient quantity to supply stoichiometric amounts for reductionor precipitation of silver ion, and not merely in the low amounts usually used to promote physical development or catalytic deposition.

In our process the developing agent is retained in the silver halide layer throughout development and transfer and serves only to develop the exposed silver halide to metallic silver when the exposed. emulsion is immersed in the alkaline solution. Upon pressing the developed emulsion into contact with the receiving sheet in the presence of the silver halide solvent andthe reducing agent, the silver halide solvent permeates the developed layer and dissolves the silver halide in the unexposed and undeveloped regions of the layer. This solution diffuses to the receiving sheet or layer, and when it comes into contact with the precipitating agent, the silver halide complex is reduced or converted to an insoluble form and is retained on the receiving sheet. No development occurs in the receiving sheet nor is there any developing agent present in the receiving sheet to cause stain or discoloration in the layer containing the positive image.

Where we refer to a hardened colloid emulsion we mean that the emulsion layer should have a hardness at least as great as that obtained with gelatin containing 0.25 ounce of formaldehyde (40 percent solution diluted 1 to 3 with water) or 0.7 gram of dry formaldehyde per pound of gelatin when freshly coated, or 0.1 ounce of the solution per pound of gelatin aged 3' to 6 months.

The concentration of developing agent in the emulsion is not criticalbut may be from about 25 grams to 500 grams of developing agent per kilogram of silver nitrate converted to silver halide in making the emulsion.

The following example illustrates the formation of an emulsion coating for use in our invention:

Example An emulsion suitable for use in our process was made by preparing solutions of (A) 25 grams of gelatin in 1 liter of water at 40 C., (B) 100 grams silver nitrate in 500 cc. water at C., and (C) 35 grams of sodium chloride in 500 cc. of water. Solutions B and C were simultaneously run into solution A at a uniform rate while stirring the latter over a period of about 10 minutes; solution B preferably not being allowed to run in faster than C. Thereafter, 150 grams of gelatin in 1500 cc. of

water at 40 C. were added. The pH of the emulsion i was then adjusted to 5.0. A developing agent was added as follows: grams of 3,4dihydroxy diphenyl were dissolved in 250 cc. of methyl alcohol. This solution was slowly added to the above emulsion with stirring and as a result the developing agent became dispersed in the emulsion in minute crystals. Preparatory to coating an emulsion layer cc. of 10% formaldehyde may be added and this composition coated on a support such as paper. After drying, the product is ready for use.

This emulsion was exposed to a line image and then placed in a 3% sodium carbonate solution for about 15 seconds to develop a negative image. The excess alkaline solution was removed from the surface of the emulsion by squeegee and the emulsion layer of the exposed and developed element was then rolled into contact with a receiving sheet of common uncoated paper stock which had been bathed in a solution containing 4% of ammonia, and 3% of amino guanidine sulfate. After being in contact for 5 or 10 seconds the sheets were pulled apart and a positive image was obtained in the receiving sheet. Under certain conditions it is possible to make more than one transfer.

Our invention will be further explained by reference to the accompanying drawing. As shown therein, a support 10 of paper or other suitable material has on it a gelatino silver halide emulsion containing a non-diffusing developing agent, the exposed portions of this layer being represented at 11 and the unexposed portions at 12. After development, a silver image 13 is formed in the exposed portions of the layer as shown in the second stage of the drawing, the unexposed portions 12 being unaffected. The layer bearing the negative image is then rolled into contact with a reducing agent whereupon a positive image 15 is formed in the receiving support.

Other modifications in technique may be visualized by which the process can be applied. The receiving paper containing ammonium chloride and zinc sulfide may be squeegeed into contact with a negative layer which has been moistened with sodium hydroxide, or the aqueous sodium hydroxide may be spread between the two dry layers. The alkaline solution diffuses into the emulsion layer, promoting development by the developing agent present in the emulsion. Diffusion of the alkaline solution into the receiving sheet or layer will release NH4OH or NH: from NH4C1 by the well-known reaction. This ammonia solution then serves as the silver halide solvent, diffusing to the emulsion layer, dissolving undeveloped silver halide from unexposed areas, and transporting it back to the receivingsurface where it is insolubilized by the precipitant.

In a further modification of our invention the sensitive layer and the receiving sheet may be combined in the form of a roll film for use in ordinary roll film cameras. When our method is used in this way the interleaving or backing paper of the roll film would be replaced by a special receiving sheet to which the positive image would be transferred during processing. Alternatively, the film spool might carry a single web, bearing on one side the light-sensitive silver halide emulsion and on the reverse side the receiving surface for the positive image. In the first case, the receiving or interleaving sheet would be impermeable to actinic light; in the second case, between the silver halide emulsion and the receiving layer there would be a light impermeable layer to prevent exposure during handling of the roll film in use.

Thus, in the spooled camera film, the special receiving sheet fulfills the functions of the conventional backing paper to protect the light-sensitive silver halide emulsion from exposure during handling outside the camera, serves as a leader for threading through the camera or the processing equipment and also serves as the receiving sheet for the positive image. It is in a suitable position relative to the emulsion so that conventional camera exposure is not impeded. The receiving sheet is also of such a nature in the dry state that it is inert to the photographic emulsion with which it comes in contact during storage prior to use.

A roll film constructed in this Way is shown in Figure 2 of the drawing.v As shown therein, 16 represents the usual transparentor opaque film support and 17 represents the silver halide emulsion: layer containing a developing agent. The interleaving or backing paper 18 is shown as an opaque duplex paper having thereon the receiving layer 19 for the positive image formed by transfer. The backing paper 18 may, of course, be constructed in various ways as by having a light impervious intermediate layer or backing layer and. may have a white reflecting layer between the support and the receiving layer 19 for purposes of viewing the positive image.

In processing the exposed roll film material, the spool is removed from the camera in the normal way and transferred to a simple processing tank which can be made light-tight and which has two or more spools for winding the exposed film through the processing bath. The exposed roll film is placed in position on one of the cranks and unrolled sufiiciently so that the interleaving leader or receiving sheet can be threaded through the tank to the take-up roll. The film is then wound through the processing; solution under conditions such that the emulsion. is developed and: the emulsion and receiving sheet,

both wet with solution, brought into close and firm contact on the take-up roll. It is also possible to use a processing apparatus having containers for two baths so that the film can be wound from a developing bath, for example, into a separate fixing bath or stabilizing solution.

When the roll film material is to be processed in this Way, the silver halide emulsion of the roll film may contain a non-diffusing developing agent as described earlier and the receiving sheet may contain a precipitating agent such as zinc sulfide. A single processing bath of alkaline hypo or alkaline sulfite then sufiices for development of the exposed emulsion.

The roll film material may also employ an emulsion free of developing agent in which case it is processed by the solvent transfer method. The silver halide emulsion in this case is of the conventional type and should be coated somewhat thinner than normal. The receiving paper bears on the receiving surface suitable nuclei to promote physical development, for instance, colloidal silver, colloidal gold, silver sulfide, and the like. The processing solution in this case is a conventional blackand'white developer containing a suitable quantity, say 20 grams per liter of sodium thiosulfate. It may be desirable to increase the pH above the normal ranges of developer solutions by the addition of alkali, to add suitable antifoggants such as benzotriazole, or to employ other means to control development rate, all of which are wellknown in the art. Alternatively, it may be desirable to employ two-solution treatment in which case the first tank would contain a conventional black-and-white developer modified as indicated if necessary and the second tank would contain a suitable solution of hypo, possibly at reduced pH.

Our invention includes all modifications and equivalents falling within the scope of the appended claims.

We claim:

1. A process for producing direct positive photographic images by transfer of a silver compound from a lightsensitive layer to a light-insensitive layer, which comprises exposing to an object or image a photographic emulsion layer of hardened colloid containing silver halide and a silver halide developing agent which is substantially nondiffusing in said colloid, treating said emulsion with an alkaline solution to initiate and promote development by the developing agent incorporated in said emulsion, and, while said emulsion layer is wet with said solution, pressing it into contact with a light-insensitive receiving support while there is at least on the surface of said support a silver halide solvent and a silver precipitating agent.

2. A process for producing direct positive photographic images by transfer of a silver compound from a lightsensitive layer to a light-insensitive layer, which comprises exposing to an object or image a photographic emulsion layer of hardened colloid containing silver halide and a silver halide developing agent which is substantially non-diffusing in said colloid, and treating said emulsion with an alkaline solution to initiate and promote development by the developing agent incorporated in said emulsion and simultaneously, while said emulsion layer is wet with said solution, pressing it into contact with a lightiusensitive receiving support while there is at least on the surface of said support a silver halide solvent and a silver precipitating agent.

3. A process for producing direct positive photographic images by transfer of a silver compound from a lightsensitive layer to a light-insensitive layer, which comprises exposing to an object or image a photographic emulsion layer of hardened gelatin containing silver halide and a silver halide developing agent which is substantially nondifi'using in said gelatin, treating said emulsion with sodium carbonate solution to cause development of a silver image in said emulsion, and then, while said emulsion layer is wet with said solution, pressing said emulsion layer into contact with a light-insensitive receiving support having at least a surface coating of a silver halide solvent and a silver precipitating agent.

4. A process for producing direct positive photographic images by transfer of a silver compound from a lightsensitive layer to a light-insensitive layer, which comprises exposing to an object or image a photographic emulsion layer of hardened gelatin containing silver halide and 3,4-dihydroxy diphenyl as a silver halide developing agent which is substantially non-diffusing in said gelatin, immersing said emulsion in a sodium carbonate solution to cause development of a silver image in said emulsion layer, and then, while said emulsion layer is wet with said solution, pressing said emulsion layer into contact with a light-sensitive paper stock having a coating of an ammonium compound and amino guanidine sulfate at least on its surface, thereby forming a positive image on said paper stock.

5. A light-insensitive receiving sheet for transfer of a silver compound image from an exposed silver halide emulsion by diffusion, comprising a paper stock containing an ammonium compound and amino guanidine sulfate.

References Cited in the file of this patent UNITED STATES PATENTS 2,196,133 Webb Apr. 2, 1940 2,388,894 Yackel et al Nov. 13, 1945 2,409,959 Ryan et a1 Oct. 22, 1946 2,500,421 Land Mar. 14, 1950 2,563,387 McCune Aug. 7, 1951 2,565,377 Land Aug. 21, 1951 2,592,368 Yackel Apr. 8, 1952 2,647,056 Land July 28, 1953 

1. A PROCESS FOR PRODUCING DIRECT POSITIVE PHOTOGRAPHIC IMAGES BY TRANSFER OF A SILVER COMPOUND FROM A LIGHTSENSITIVE LAYER TO A LIGHT-INSENSITIVE LAYER, WHICH COMPRISES EXPOSING TO AN OBJECT OR IMAGE A PHOTOGRAPHIC EMULSION LAYER OF HARDENED COLLOID CONTAINING SILVER HALIDE AND A SILVER HALIDE DEVELOPING AGENT WHICH IS SUBSTANTIALLY NONDIFFUSING IN SAID COLLOID, TREATING SAID EMULSION WITH AN ALKALINE SOLUTION TO INITIATE AND PROMOTE DEVELOPMENT BY THE DEVELOPING AGENT INCORPORATED IN SAID EMULSION, AND, WHILE SAID EMULSION LAYER IS WET WITH SAID SOLUTION, PRESSING IT INTO CONTACT WITH A LIGHT-INSENSITIVE RECEIVING SUPPORT WHILE THERE IS AT LEAST ON THE SURFACE OF SAID SUPPORT A SILVER HALIDE SOLVENT AND A SILVER PRECIPITATING AGENT.
 5. A LIGHT-INSENSITIVE RECEIVING SHEET FOR TRANSFER OF A SILVER COMPOUND IMAGE FROM AN EXPOSED SILVER HALIDE EMULSION BY DIFFUSION, COMPRISING A PAPER STOCK CONTAINING AN AMMONIUM COMPOUND AND AMINO GUANIDINE SULFATE. 